1. Field of the Invention
This invention relates to hot gas generating apparatus, and more particularly to an incinerator apparatus for burning combustible materials for the generation of hot gases for use outside the apparatus. The invention specifically relates to an improved incinerator for the complete and clean burning of waste combustibles and combining the hot combustion gases with incinerator cooling air to provide a hot gas mixture suitable for use in heating and drying processes and the like.
2. Description of the Prior Art
The term "incinerator" has generally been employed to designate a device for burning waste products as a means of waste disposal. In the prior art incinerators, the hot gases produced during combustion generally have been discharged into the atmosphere, with little or no attempt being made to utilize the energy released by the combustion process. These devices are distinguished from furnaces in which fuel is burned for the generation of hot combustion gases which are then used to heat a second medium, through a heat exchanger or heat exchange surface, with the thermal energy normally being transferred by the second medium for use in processes outside the furnace. Thermal losses in such furnaces are, of course, always encountered in the transfer of heat between the combustion gases and the second medium.
Combustion air pre-heaters and the like are frequently employed with both furnaces and incinerators to try to salvage, or scavenge, waste heat, but such devices are relatively expensive both to purchase and to operate, and are only effective to a limited degree.
The increased emphasis on reduction of air pollution has resulted in greater emphasis being placed upon the assurance of complete or clean combustion in incinerator devices such as those used at municipal incinerator plants, industrial processes, and the like. Accordingly, a number of new incinerator devices have recently been developed, one such device being illustrated, for example, in U.S. Pat. No. 3,771,469. This device employs a horizontally-disposed cylindrical combustion chamber with an exhaust outlet in one end wall leading to a stack which discharges into the atmosphere. Burnable waste material and combustion air is discharged into the refractory-lined combustion chamber through a tangential opening adjacent the other end wall, with combustion taking place as the material moves in a swirling or vortical pattern around and through the chamber into the exhaust outlet. Additional fuel may be supplied through a nozzle arrangement including means for supplying additional combustion air for the fuel to assure burning of wet or hard-to-burn combustible materials. Vortical movement within the combustion chamber carries unburned particulate solids from the combustion chamber through the exhaust outlet.
In the operation of conventional furnaces, air in the combustion chamber in excess of that required for stoichiometric combustion of the fuel generally must be held to a minimum since such excess air absorbs thermal energy which could otherwise be transferred to the working fluid. This absorbed energy is lost as the excess air and combustion gas pass out of the system as exhaust. Combustion air supplied in quantities less than that required for stoichiometric combustion causes incomplete burning of the fuel with the result that excess quantities of unburned fuel and carbon monoxide are present in the stack gas. Further, the production of carbon monoxide instead of carbon dioxide results in the wasting of substantial quantities of the available energy in hydrocarbon fuels. Some excess air is therefore normally provided in order to promote total combustion and to control the temperature of combustion to avoid the production of nitrogen oxide pollutants which are formed only at very high temperatures. However, careful control of the excess air must be maintained in order to balance the opposing factors in the conventional furnace design.